Production of perforated non woven fibrous webs

ABSTRACT

PERFORATED NON-WOVEN FABRICS ARE PRODUCED BY FORMING A FIBROUS WEB CONTAINING A BINDER, FORMING ELONGATED SLITS IN SAID WEB, PARTIALLY SETTING THE BINDER, STRETCHING SAID WEB TRANSVERSELY OF SAID SLITS WHEREBY SAID SLITS FORM HOLES, AND COMPLETING SETTING OF SAID BINDER WITH SAID WEB IN STRETCHED CONDITION WHEREBY SAID WEB IS BONDED AND RETAINS SAID HOLES EVEN UPON RELEASE OF THE STRETCHING FORCE.

w. HELING PRODUCTION OF PERFORATED NON-WOVEN FIBROUS WEBS Filed Nov. 17,1970 Sept. 4, 1973 INVENTOR WILHELM HELING BURGESS. DINKLAGE 8. SPRUNGATTORNEYS.

FIG. 2.

United States Patent US. Cl. 162-114 7 Claims ABSTRACT OF THE DISCLOSUREPerforated non-woven fabrics are produced by forming a fibrous webcontaining a binder, forming elongated slits in said web, partiallysetting the binder, stretching said web transversely of said slitswhereby said slits form holes, and completing setting of said binderwith said web in stretched condition whereby said web is bonded andretains said holes even upon release of the stretching force.

The present invention relates to the production of perforated non-wovenfabrics, i.e. non-woven fabrics provided with holes.

Non-woven fabrics are being used today for many purposes. For theirmanufacture, a mat is first prepared and then sprayed or impregnatedwith a binding agent. Then the mat thus impregnated is subjected to aheat treatment wherein the binding agent, latex for example, is set orvulcanized. The sheet material thus preparedhas good resiliency and canbe used as a stiffening insert, i.e. interfacing, or for many otherpurposes, e.g., as throw-away cloths.

In other applications it is desirable to produce a pattern of holes inthe final product. This, however, requires a considerable investment inequipment. First the mat must be laid on a sieve and then be coveredwith a perforated plate, somewhat in the manner of US. Pat. 2,861,251.Then strong jets of water are shot from above through the holes in theplate. The water driven with great force through the holes pushes asidethe fibers therebelow and then exits through the sieve. The mat thusperforated is still not very stable and must then be impregnated, at anadditional great investment in equipment, so that it will bestrengthened.

It has now been found that non-woven fabrics containing holes in anydesired pattern can be prepared very simply by first suspending thefibers in a very great excess of water (about :1 part fibers to 1000parts water), as is done in the manufacture of paper.

The water also contains a binding agent, e.g., latex. It is desirable tocoagulate the latex, because then the precipitated binding agentdeposits itself preferentially on the surface of the fiberssimultaneously suspended in the water. Then the fiber suspensioncontaining the binding agent is poured onto a screen, e.g., a screen asdescribed in Voith Forschung und Konstruktion, No. 16, May 1967, ArticleNo. 12, reprint 1782, thereby forming a coherent web of fibers.

The coagulation of the binding agent can be brought about by theaddition of acid or salts or by the electrical reversal of the charge ofthe binding agent dispersion, using known methods. The use ofheat-sensitized latices is also possible. Here the binding agentcoagulates as soon as a certain temperature is reached, which can bevery low, e.g., 35 C.

Basically, the prior coagulation of the binding agent onto the fiberscan be omitted. In this case, of course, considerably more binding agentmust be added, because when the mixture is poured onto the screen alarge part of the binding agent is lost with the Water. If, however, itis Patented .Sept. 4, 1973 first coagulated, nearly all of the bindingagent deposits on the -fibers, so that, when the mixture is poured ontothe screen, almost nothing but pure water flows through the screen. v

After a wet continuous mat of fibers containing binding agent hasformed, the mat is first drained as well as possible. Then the mat,still wet, is placed on a suitable support and provided with a pluralityof small slits. The slits may have, for example, a length of 2 to 8 mm.At a distance of the same order of magnitude, the second slit is made,until a whole row of slits is produced. At a distance of a fewmillimeters from the first row of slits a second row of slits iscreated, preferably in such a manner that an offsetting of the slitsresults, i.e. the slits are staggered. The slits can be produced withfine spring blades or with rollers having razor-blade-like segments.Apparatus suitable for the slitting of plastic sheet materials can beused for the instant slitting operation.

. The invention will be further described with reference to theaccompanying drawings wherein:

FIG. 1 is a schematic plan view of a fiber web which has been slit; and

FIG. 2 is a schematic plan view of the web after it has been partiallyset, stretched transversely of the slits and setting of the binder hasbeen completed.

Referring now more particularly to the drawing, a nonwoven fleece or mat11 containing binder is laid down in paper making fashion as describedhereinabove and the wet fleece is slit to provide staggered rows ofslits 12.

Either before or after the slitting operation, the mat is given apreliminary drying on a cylinder or drum dryer to such an extent that itcontains only to moisture (with reference to the fiber weight). Then, inthe final drying process at about 130-160 C, it is stretched by about 30to 50% transversely of the slits and at the same time dried. This widensthe slits to holes 13 of generally diamond-shaped configuration as canbe seen in FIG. 2. Since at the same time a vulcanization or setting ofthe binding agent takes place the holes are stabilized. The end productin certain embodiments resembles expanded metal structures in that thebonded web turns up sideways between openings 13 to give athree-dimensional effect.

The invention will be further described in the following illustrativeexample wherein all parts are by weight unless otherwise stated.

EXAMPLE 2.5 kg. of 3 denier rayon fibers 10 cm. long and 2.5 kg. of 6denier nylon fibers 20 cm. long are dispersed in 10 liters of water. Tothis dispersion there are added 2 kg. of Butofan KR 2345 which is acoagulatable butadiene-acrylonitrile latex sold by Farbenfabriken Bayer.Then there are added 0.08 kg. of Pol-imin SN 20 which is a coagulantcausing the Butofan to coagulate. The coagulated latex is therebydeposited on the surface of the fibers. With continuous stirrin the thusprepared fiber slurry is poured onto a Hydroformer Steigsieb, sold bythe German firm Voit cif Heidenheim, i.e. the suspension is poured ontoa moving sieve having a width of 1.5 m. at such a speed that theresulting nonwoven on the screen has a weight of 50 g./m. By suction thestill wet fleece is freed from as much water as possible, i.e. down to200% of water based upon the fiber weight. Then the still wet fleece isforwarded onto a backing consisting of foamed rubber. Here the sheetstructure is slit with a slittling machine as described in Czech Patent114,838, the slits having a length of 4 mm. The distance between slitsin the same line is 3 mm.; the lateral distance between adjacent linesof slits is 2 mm.

Subsequently the thus slit fleece is dried on a drum dryer, the metalsurface of which is heated to C fiber-weight. Thenthe fleece-isforwarded to a tenter frame wherein the width of the fleece band isexpanded from 1.5 to 2.4 m. whereupon the slits are converted intodiamond like openings. Originally the length of a slit is 4 mm. butafter the expansion the length is only 3 mm. but, on the other hand, theoriginal width which is practically zero is brought to 2 mm. Thetemperature of the air in the tenter frame is 140 C., the binderthereupon setting so that even upon removal from the frame the fabricmaintains its shape and three-dimensional appearance.

The fibers suitable for practicing the invention include syntheticfibers such as nylon, polyester, acrylics, olefins, cellulosics such asacetate, rayon, and the like, as well as natural fibers such as cotton,wool, and the like, and blends thereof. Their deniers and lengths may bevaried widely. The fibers may be laid down into the initial fleece bythe wet lay process described hereinabove or by the known dry layprocesses, involving air deposit or crosslaying of carded laps. Thebinder may be included in the liquid in the event of Wet laying or itmay be subsequently applied by spraying, coating or the like; in thecase of dry laying by air deposit the binder may be depositedsimultaneously with the fibers or it may be postapplied as bysprinkling, liquid impregnation, spraying or foam impregnation. If thebinder is applied as a dry solid, the initial partial setting may beachieved by a light heating to render tacky the outside of the binderparticles. The type and proportion of binder to fiber may also varywidely as is known in the non-woven art depending upon the intended enduse and desired hand.

As noted, the partial setting may be effected either before or afterslitting. If the water content is very high it may be desirable toprovide a resilient backing to facilitate slitting before partialsetting. The slitting itself can be effected by localized melting in thecase of fusible fibers although it is preferably effected by cutting.

The extent of transverse stretching depends upon the proportion of holesdesired in the final structure and the disposition and arrangement ofthe slits. Drying or completion of setting of the binder is of courseeffected with the fabric in stretched condition so as to retain theexpanded, perforated or open configuration.

In contrast with existing perforated non-Wovens wherein the action ofwater jets to displace fibers and form holes causes bunching up offibers about the holes, the new fabric is characterized by asubstantially uniform distribution of fibers throughout the fabric, evenaround the holes. The three-dimensional effect gives a unique hand andappearance not heretofore realized with fiber products.

It will be appreciated that the instant specification and examples areset forth by way of illustration and not limitation, and that variousmodifications and changes may be made without departing from the spiritand scope of the present invention.

What is claimed is:

1. Process of producing perforated non-woven fabrics which comprisesforming a non-woven fibrous web containing a binder, forming elongatedslits in said web, partially setting the binder, stretchin said webtransversely of said slits whereby said slits form holes, and completingsetting of said binder with said web in stretched condition whereby saidweb is bonded and retains said holes even upon release of the stretchingforce.

2. Process according to claim 1, wherein said slits are provided in aplurality of staggered rows.

3. Process according to claim 1, wherein said web is wet and is dried toa water content of approximately to based on the weight of fiber,thereby to effect partial setting of said binder, completion of settingbeing effected by completion of drying.

4. Process according to claim 1, wherein said slits range in length fromabout 2 to 8 mm. and are arranged in rows where they are spaced fromadjacent slits by about 2 to 8 mm.

5. Process according to claim 1, wherein the web is formed by suspendingfibers in water containing a binder, and pouring the suspension onto ascreen to leave a wet binder-containing web.

6. Process according to claim 5, wherein the binder is in the suspensionin coagulated condition.

7. Process according to claim 6, wherein the wet binder-containing webis dried to a water content of approximately 80 to 100% based on theweight of fiber, thereby to effect partial setting of said binder,completion of setting being effected by completion of drying, said slitsranging in length from about 2 to 8 mm. and being arranged in staggeredrows in which they are spaced from adjacent slits by about 2 to 8 mm.

References Cited UNITED STATES PATENTS 3,293,104 12/1966 Hull 156-229 X3,042,576 7/1962 Harmon et al 162-114 2,697,678 12/1954 Ness et al.156229 X 3,253,317 5/1966 Such 162-114 X S. LEON BASHORE, PrimaryExaminer A. L. CORBIN, Assstant Examiner US. Cl. X.R.

19l6l P; 156229, 252; 162--197

